Apparatus for producing cellulose acetate



Feb. 10, 1931.

J. ALTWEGG APPARATUS FOR PRODUCING CELLULOSE ACETATE Filed'Oc t Patented Feb, 10, 1931 UNITED STATES PATENT OFFICE JEAN ALTwEGGroF FREIB'CRG, GERMANY, ASSIGNOR T0 E. I. DU PON'I. DE NE'MOURS & CQMPANY, OF WILMINGTON, DELAWARE, A CORPORATION DELAWARE APPARATUS FOR PRODUCING CELLULOSE ACETATE Original application filed May 5, 1927, Serial No. 189,100. Divided and'this application filed October 10,

' 1929. Serial No. 398,739.

This invention relates to an apparatus for producing cellulose acetate and is a division of application Serial No. 189,100, filed May 5, 1927-.

The technical processes most often used for the manufacture of cellulose acetate consist in causing acetic anhydride to react upon taneously. The operation is carried out,

preferably, in the presence of a certain quantity of a catalyzing agent, such as mineral acids, certain organic acids, metallic halogenated compounds, etc. As diluting agent, a liquid solvent of cellulose acetate, is added, such, for instance, as glacial acetic acid. The whole of this acetylating liquor maybe added at one time or in several portions during the course of the operation. Moreover, the diluti-ng agent may be added first and the acetylat ing agents, properly so called, may be added afterwards. The reaction is carried out at different temperatures. Generally, a low temperature is used-at the beginning, the operation being brought to completion at a higher temperature. During this operation the reacting mass is energetically stirred.

The reaction so conducted presents the special problem that the consistency and 'the structure of' the reacting mass continuously and deeply changes during the operation. At the beginning of the operation the intact fibre,

' merely wetted, is being dealt with. Little by little this fibre swells and forms an extremely tenacious magma. Later, the swelled fibre dissolves and the mass becomes more flowing, assuming towards the end of the operation the form of a transparent, more or less fluid /tus usually employed for this purpose are generally very powerful kneading mixers which subject the material to an actual grinding. These apparatus must be powerful. In

fact, during the first phase the intact fibre has a tendency to jam the arms of the mixer and during the second phase, where all the mass is in the form of a thick magma, great mechanical effort must be exerted in order to perform the mixing. During the whole of the last phase, during which the product of the reaction is more or less fluid, the mixer is not at all a suitable apparatus.

It has been ascertained by applicant that it is much more efficient to perform the acetylation in an apparatus provided with different stirring devices adapted to the consistency of the mass at each phase of the reaction and, according to the present invention, the mass is caused to pass through an apparatus provided with difierent'kinds of mixing devices, At the same time, in such an arrangement a continuous progression of the acetylation is obtained, the fibre and acetylating liquor being introduced at one end and the finished gum leaving the apparatus at the other end. The mixing devices which are suitable for the first or fibrous phase are points or hook-like munbers presenting a small area which'catch and tear the fibre without kneading or squeezing it. The mix-- ing takes place in this manner with very little effort, without risk of jamming orseizing. For the thick phase strong mixers of simple form which act as kneaders are used. Finally, for the gum phase the mixing is done by means ofpaddles or scull-shaped members. The passage of the mass'from one consistency to another not being sudden and forcible but progressing by intermediate stages, similarly the transition from one mixing system to another may take place byv intermediate systems.

As an example, one can give to the acety lating apparatus" the form of a practically vertical tube or of a column provided with a central shaft which carries stirring members rotating horizontally. The cellulose fibre and the acetylating liquor are introduced at the top of the column and the cellulose acetate gum is continually extracted at the lower portion.

The drawingaccompanying and forming part of this specification illustrates in vertical central section, by way of example only, one form of apparatus which may be used for carrying the present invention into practice. In this form the apparatus comprises a vertical tube or cylinder 1 having a central shaft 2 mounted for horizontal rotation in said cylinder, the cylinder being provided in its cover with a. tubular inlet 14; through which the cellulose fibre and ace'tylizing' fluid may be charged, while a tubular outlet port 15 is provided inthe bottom of the cylinder through which the cellulose acetate may be continuously drawn off. Secured to the shaft for rotation therewith are a plurality of agitating members 3, 1, 5, 6, 7, 8, 9, 10, 11, 12 and 13, said members being divided into several distinct groups, the individual members of each group varying in size and form from those of the remaining groups. For instance, the group nearestthe upper or intake end of the apparatus comprises a pairof comparatively slender arms 3. The next succeeding group comprises a pair of similar arms 4 bent into hook shape, preferably in opposite di-.

rections, at their respective free ends. The third group comprises a pair of similarly slender arms 5 which are respectively forked at their free ends, it being understood that the invention is not limited to the exact formation at the ends of the arms of this or any of the other groups, since this may be varied as seems desirable. The fourth group comprises three pairs. 6, 7 and S, of

similarly formed members having pointed ends, the members of the succeeding pairs being progressively stouter. The fifth group again comprises three pairs 9, 10 and 11, of similarly formed members, the ends of these members being in the form of paddles. the paddles of the last pair being larger than those of the preceding pair. The sixth and last group comprises two pairs, 12 and 13, of

of stirring member which is best adapted for,

the structure ofthe mass at that particular stage. Moreover, at those points where the mass would tend to rotate with the shaft, for instance in the spaces between the stirring members, a series of stationary bailies or deflectors 16 is provided, these bafiies being shown in the present instance extending inwardly from diametrically opposite sides of the cylinder, those at one side being in staggered relation to those at the opposite side.

The temperature of the mass, as it passes through the cylinder, may be,-easily regulated. This may be accomplished, if desired, by providing the cylinder with water jackets or pipes disposed within the cylinder in which liquids at the desired temperature may be caused to circulate or, as shown in the drawing, irrigation pipes 17, 18 and 19 may encircle the cylinder, from Which pipes the liquids may be caused'to flow over the outer surface of said cylinder. The traps 20, 21 and 22 have discharge pipes 28, 24 and 25 provided for catching and disposing of the liquids passing down from the pipes 17, 18 and- 19 respectively. A well-defined region of the cylinder or column can thus be cooled orheated at will thereby obtaining a constant temperature for each phase of the reaction.

The cylinder may, if desired, be of different diameters at different parts thereof. For instance, at places Where slow passage of the mass is desired, the diameter of the cylinder may be comparatively large while at places where rapid progress is desired the diameter may be reduced thereby to facilitate rapid heatingor cooling. Moreover, the cylinder, instead of being a single structure as shown herein, may comprise a plurality of sections through which the mass may be caused to pass in succession.

It is believed that the operation of the apparatus will be obvious from the foregoing. description. The cellulose fibre and the acetylating agents are fed into the cylinder at the top thereof. The simplest manner of feeding is to introduce the cellulose fibre and all of the acetylating agents at once. When special qualities are desired, however, pipes may be disposed so as to deliver parts of the acetylating agents to any desired zone in the length of the cylinder. In this way the effect of the familiar acetylation methods by which the acetic acid and the anhydrid are caused to act separately on the fibre may be obtained.

The apparatus herein described permits the operation to be carried on under specific and exact temperatures and provides special stirring for each stage. In addition, it makes it possible to obtain accurately cellulose ace tates possessing predetermined degrees of viscosity, clearness of solution, solubility etc. The size of the apparatus is reduced tothe minimum as the same is completely filled throughout the operation, so that there is no chance of any unused space to cause trouble while the continuity of'operation avoids loss of time in charging and discharging.

I claim:

1. An apparatus for manufacturing cellulose acetate which comprises a column having an inlet adjacent one end and an outlet adjacent the opposite end, and a plurality of rotatable stirring elements disposed within said column, the elements varying in form and increasing in size from inlet to outlet according to t e texture of the material to be treated by said elements.

2. An apparatus for manufacturing cellulose acetate which comprises a column having an inlet adjacent one end and an outlet adj acent the opposite end, a plurality of rotatable stirring elements disposed within said column, the elements varying in form and increasing in size from inlet to outlet according to the texture of the material to be treated by said elements, and means disposed within the column for opposing rotary movement of a mass ofmaterial in the col- 3. An apparatus for manufacturing cellulose acetate which comprises a column having an inlet adjacent one end and an outlet adjacent the opposite end, a shaft mounted for rotation in said column, a plurality'of stirring members carried by said shaft and extending radially of the column, the members varying in form and increasing in size from inlet to outlet according to the texture of the material to be treated by said members.

4. An apparatus for manufacturing cellulose acetate which comprises a column having an inlet adjacent one end and an outlet adjacent the opposite end, a shaft mounted for rotation in said column, a plurality of stirring members carried by said shaft and extending radially of the column, these members varying in form and increasing in size from inlet to outlet according to the texture of the material to be treated by said members, and baflies extending from the wall of the column toward the center thereof between adjacent stirring 40 members.

5. An apparatus for manufacturing cellulose acetate which comprises a column'having an inlet adjacent one end and an outlet adjacent the opposite end, a shaft mounted for rotation in said column, a plurality of stirring members carried by said shaft and extending radially of the column, these members varying in form and increasing in size from inlet to outlet according to the texture of the ma 1 terial to be treated by said members, and

battles disposed at diametrically opposite sides of the column and extending toward the cen ter thereof, the baffies at one side being dis-' posed in staggered relation to those at the opposite side.

In testimony whereof, I have affixed my signature to this specification.

JEAN ALTWEGG. 

